Chain Length calculator

Discussion in 'Bicycle Mechanics and Repairs' started by Smokin Joe, 18 Nov 2008.

  1. Smokin Joe

    Smokin Joe Legendary Member

    The question of "What length should my chain be?" often crops up here and in Beginners. This very useful site takes the guesswork out of it, and inputting my own data gave me the answer (53 links) that I had arrived at through trial and error and lots of bad language.

    It might make a worthwhile sticky.

    http://www.machinehead-software.co.uk/bike/chain_length/chainlengthcalc.html
     
  2. jimboalee

    jimboalee New Member

    Location:
    Solihull
    Go to Shimano Cycling website Europe.

    Go to Tech Docs.

    Go for any Rear derailleur. Dura Ace will do.

    The instruction sheet opens in Adobe.


    There are two methods, both are described on the sheet.


     
    C R likes this.
  3. kyuss

    kyuss Veteran

    Location:
    Edinburgh
    Surely the easiest way is the Sheldon way. To hell with chainstay measurements and cog sizes, just wrap the chain round the big big combination without going through the derailleur and mark the closest point it can be joined then add one complete link. I've always done it this way and never had a chain too long or too short.
     
  4. OP
    OP
    Smokin Joe

    Smokin Joe Legendary Member

    There are a variety of ways you can use, but for someone who has no idea it is a very useful reference guide.
     
    ozboz likes this.
  5. Chain length surly will depend on chain ring size, cassette size and chainstay length (bottom bracket to axle), unless you can write a program that allows you to input all these sizes and measurements and then factor in free play allowances I don't see how you could have a one program fits all.

    There are as mentioned several different methods, my prefered is wrap chain over big ring and also biggest rear sprocket, then add 2 links to where they meet, seems to work perfectly well for me and friends.
     
  6. OP
    OP
    Smokin Joe

    Smokin Joe Legendary Member

    If you follow the link, that's exactly what it does.
     
  7. jimboalee

    jimboalee New Member

    Location:
    Solihull
    P181108_1857.jpg

    The Shimano method. :eek:
     
  8. OP
    OP
    Smokin Joe

    Smokin Joe Legendary Member

    Exactly what you get with the calculator, without having to thread the chain through then take it off again to cut it.

    Each to his own.
     
  9. stevew

    stevew Well-Known Member

    Location:
    Orpington
    If you are trying to go outside the manufacturers specs regarding the chain wrapping ability of a given derailleur combination you will have to be sure the "big big" combination is always possible otherwise there could be dire consequences ! Maybe the chain will be a little loose on the "small small" combination but all will be relatively safe. Had to do this on my 'bent recently as I was 2 teeth over the recommended chain wrap ability of the rear derailleur. All works fine and I try to avoid the "small small" if I can remember !!
     
    Ajax Bay likes this.
  10. jimboalee

    jimboalee New Member

    Location:
    Solihull
    The chain NEVER goes big-big or small-small. This is called 'crossing up'.

    www.machinehead-software.co.uk/bike/gears/gear_calculator.html

    Let me use MachineHead to illustrate how gear combinaions work.
    Notice 'Gear Usage Table'.
    It is a long drawn out tell, and MachineHead is swiftly to hand.

    Using Shimano's diagram, all gear combinations will be attainable.
     
  11. stevew

    stevew Well-Known Member

    Location:
    Orpington
    The chain definitely does go "big big" & "small small" you have only to watch some less experienced cyclists to see this. It might not be a good thing to do but it often happens !
    Also on a 'bent with about a metre of chain between the rear mech and the chain guide pulley it really causes no problems as the chain angles are too small to even consider.
    So in the real world it DOES happen.
    In the ideal world of standard DF bikes it SHOULDN'T happen.
     
    Ajax Bay likes this.
  12. Yup.
     
  13. Shirley quicker to slap the chain on, measure it and then chop it than count your teeth, measure your stays, faff around with a calculator and count the links?

    Each to his own..
     
  14. Dave5N

    Dave5N Über Member

  15. Dave5N

    Dave5N Über Member

    Unless it's a new or rebuild, I just hold the new one updangling next to the old one, and cut accordingly. If it worked before it'll work again. If anything's change with gears or frame, I just wrap it round a la Sheldon.
     
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